This invention relates to an inert gas supply arrangement for a printer. In particular, this invention related to an inert gas supply arrangement for a printer that incorporates a number of ink jet printheads. The ink jet printheads each have at least one printhead chip.
As set out in the material incorporated by reference, the Applicant has developed ink jet printheads that can span a print medium and incorporate up to 84 000 nozzle assemblies. Furthermore, the printheads are able to generate text an images at speeds of from 20 ppm up to 160 ppm, depending on the application.
These printheads includes a number of printhead chips. The printhead chips include micro-electromechanical components, which physically act on ink to eject ink from the printhead chips. In order to achieve the necessary movement, the components incorporate thermal bend actuators. These use differential heat expansion to generate the necessary movement.
It is important to note that the components are microscopic. It follows that heat expansion is far more dramatic than at the macroscopic scale. The components are required to operate at very high speeds in order to achieve the print rate mentioned above. In commercial applications, these high speeds must be maintained for long periods of time. Applicant has found that the printhead chips operate most efficiently at a high heat. However, oscillatory movement at high speed and high heat for extended periods of time can create fatigue damage. This is particularly the case where the components include metal, as is the case with many of the printhead chips developed by the Applicant.
Applicant has found that oxidation tends to occur when the components are operated at temperature, which would otherwise be optimal. Accordingly, the Applicant has conceived the present invention to address the problem of oxidation at the high temperatures. As a result, the Applicant has developed a printer that has printheads that are capable of operating at optimal temperatures while avoiding oxidation.
The overall design of a printer in which this invention is applied is based on the use of replaceable printhead modules. The modules are in an array approximately 8 inches (20 cm) long. An advantage of such a system is the ability to easily remove and replace any defective modules in a printhead array. This eliminates having to scrap an entire printhead if only one chip is defective.
A printhead module in such a printer can be comprised of a xe2x80x9cMemjetxe2x80x9d chip, being a chip having a vast number of the nozzle assemblies mentioned above. The components, which act on the ink, are can be those as disclosed in U.S. Pat. No. 6,044,646, incorporated by reference. However, other chips may also be suitable.
The printhead might typically have six ink chambers and be capable of printing four-color process (CMYK) as well as infrared ink and fixative.
Each printhead module receives ink via a distribution molding that transfers the ink. Typically, ten modules butt together to form a complete eight-inch printhead assembly suitable for printing A4 paper without the need for scanning movement of the printhead across the paper width.
The printheads themselves are modular, so complete eight-inch printhead arrays can be configured to form printheads of arbitrary width.
Additionally, a second printhead assembly can be mounted on the opposite side of a paper feed path to enable double-sided high-speed printing.
According to the invention, there is provided a printing assembly that comprises
a printing unit; and
an inert gas supply that is connected to the printing unit to provide components of the printing unit with inert gas.
The printing unit may have at least one thermally actuated ink jet printhead. The ink jet printhead may incorporate micro-electromechanical components for the ejection of ink. The micro-electromechanical components may be thermally actuated.
The printing unit may include a printhead assembly that has at least one printhead chip and defines an inert gas inlet. The at least one printhead chip may comprise a plurality of nozzle assemblies positioned on a wafer substrate, each nozzle assembly having nozzle chamber walls and a roof wall that define a nozzle chamber and an ink ejection port in fluid communication with the nozzle chamber and a micro-electromechanical actuator that acts on ink within the nozzle chamber to eject ink from the nozzle chamber.
A conduit assembly may be arranged within the printing unit to provide an inert gas conduit from the inlet to the at least one printhead chip. The conduit assembly may be configured so that inert gas pumped into the conduit assembly provides an inert operating environment for the printhead assembly. An inert gas supply device may be connected to the printing unit at the inlet to supply the conduit assembly with inert gas.
The printing unit may include a number of printhead chips, and a number of corresponding nozzle guards that are positioned over respective printhead chips. Each nozzle guard may have a cover member and a support structure that supports the cover member over each printhead chip. The cover member may define a plurality of passages. Each passage may be aligned with a respective ink ejection port so that an ink droplet ejected from each ink ejection port can pass through the passage and onto a print medium. The support structure may define a plurality of openings so that inert gas can pass into a region between each printhead cover and its associated printhead chip and through the passages defined by the printhead cover.
The inert gas supply may be in the form of a nitrogen supply unit. The nitrogen supply unit may be a membrane nitrogen separation unit.
The printhead assembly may include an ink distribution structure that defines a plurality of printhead chip slots that are dimensioned so that each printhead chip can be positioned in a respective slot. The structure may also define a plurality of ink distribution pathways in fluid communication with each slot to supply the printhead chips with ink. The structure may further define an inert gas pathway from the inlet defined by the printhead assembly and said region between each printhead chip and its associated cover member so that the inert gas can be pumped from the inlet, through the ink distribution structure and out through the passages defined by the cover members.